Selected Acronyms
DOCSIS Data Over Cable Service Interface Specification.
DPON DOCSIS PON. See DOCSIS and PON. DPON is used to refer to a type of PON that implements DOCSIS service layer on existing Ethernet PON, MAC and PHY layers.
EPON (or GEPON) Ethernet PON.
FTTH Fiber To The Home, refers to fiber optic cable that replaces the standard copper wire of the local Telco. FTTH can carry high-speed broadband services integrating voice, data and video, and runs directly to the junction box at a home or building. Also called Fiber To The Building (FTTB), or Fiber-to-the-Subscriber (FTTx).
ONU Optical Network Unit
PON Passive Optical Network, is a point-to-multipoint, fiber to the premises network architecture in which unpowered optical splitters are used to enable a single optical fiber to serve multiple premises, typically 32-128.
RFoG (or RF-PON) “RF over Glass”—encapsulates existing RF traffic and pipes it over fiber. This is an analogue transmission over fiber as distinguished from EPON/GPON technologies.
rtPS Real Time Polling Service—a scheduling service to resolve contentions and conversely avoid collisions in data communications. Related—nrtPS Non-real Time Polling Service.
USCB mode of operation of a network—Upstream Channel Bonding.
Data Over Cable Service Introduction
Cable operators have widely deployed high-speed data services on cable television systems. These data services allow subscriber-side devices, such as personal computers, to communicate over an ordinary cable TV network Hybrid Fiber Coax (HFC) cable. Cable Television Laboratories, Inc. (CableLabs®) publishes detailed technical specifications for such systems, including DOCSIS—Data Over Cable Service Interface Specification. Referring to FIG. 1, in typical cable systems 100, a Cable Modem Termination System (CMTS) 102 (or a modular CMTS called “M-CMTS”)1 connects the cable network 104 to a data network, such as the Internet 106. A downstream QAM 110 receives data transferred from the CMTS over a packet switched portion of the network, performs modulation and other processing, and then transfers the modulated data over a Hybrid Fiber Coaxial (HFC) portion 120 of the cable network to subscribers. This is called the “downstream” direction. 1The EQAM is not included with the core in a modular CMTS. Some systems may utilize a Universal Edge QAM device, or “UEQAM” for short, which typically comprises a chassis having one or more gigabit Ethernet (GigE) input ports, and multiple QAM modulators and RF upconverters on the output (downstream) side. The present invention is applicable to all of these architectures, including both Integrated CMTS and Modular CMTS. In that regard, we use “CMTS” herein in the broad, generic sense.
In general, this HFC or coax cable feeds the last link (for example, over the last half mile or less) to an individual home or other structure. There, a cable modem (CM) 130 may provide an packet interface, for example Ethernet compliant, to various consumer premises equipment (CPE) 132 such as a personal computer. The CM may be connected to a hub or router (not shown), for example to implement a home network, wireless access, etc. The CM (or a second CM) may be implemented in other equipment, for example a “set-top-box” (STB) 140 which provides an interface to a television 142.
DOCSIS specifies that the cable modems obtain upstream bandwidth according to a request/grant scheme because the upstream channel is shared. A cable modem sends a bandwidth allocation request when it receives a packet from a subscriber device and the packet needs to be sent upstream into the cable network. The CMTS scheduler grants these requests using bandwidth allocation map (“MAP”) messages. MAP messages inform the CMs about specific allocations of upstream spectrum in the time dimension, using time slots or “minislots.” The requesting modem then waits for its scheduled time before it can begin transmission. In this way, the system avoids collisions in upstream transmissions from multiple CMs. The DOCSIS specifications also provide other scheduling modes in which the CMTS grants bandwidth to the modem without an explicit request from the cable modem. One example is the UGS (Unsolicited Grant Service) mode. Unsolicited Grant Service is an Upstream Flow Scheduling Service Type that is used for mapping constant bit rate (CBR) traffic onto Service Flows. Since the upstream is scheduled bandwidth, a CBR service can be established by the CMTS scheduling a steady stream of grants. These are referred to as unsolicited because the bandwidth is predetermined, and there are no ongoing requests being made. The classic example of a CBR application is Voice over Internet Protocol (VoIP) packets.
In addition, individual CMs are assigned to specific frequency “channels.” In this way, more than one CM may actually transmit at the same time, but they are separated by frequency division multiplexing. U.S. Pat. No. 7,386,236 (Kuo et al.) describes a multiple wavelength TDMA optical network. DOCSIS 3.0 allows a single CM to transmit on multiple upstreams (channels), as further discussed below. In other words, a DOCSIS 3.0 enabled CM would have multiple transceivers simultaneously operable at different frequencies.
Recently, especially in newer communities, service providers (or developers) are implementing fiber to the home (FTTH), in other words, running “fiber” or “glass” (optical fiber cable) all the way from the head end or distribution hub to the home. FTTH is desirable because it can carry high-speed broadband services integrating voice, data and video. Accordingly, separate traditional telephone lines (copper) may no longer be necessary. And coax to the home for internet access and television programming may be obviated as well. RF over Fiber (“RFoG”) is advantageous because the analog RF signals transmitted over fiber (in the form of photons) incur little loss, even over run lengths of many miles, whereas losses over coax can be significant, requiring the use of repeaters or amplifier equipment every 1000 to 2000 feet. Fiber is also essentially immune to EM interference and unauthorized eavesdropping. That said, RFoG presents new transmission scheduling challenges and opportunities. One aspect of the present invention is directed to improvements in upstream scheduling for RF over glass.
Several preferred examples of the present application will now be described with reference to the accompanying drawings. Various other examples of the invention are also possible and practical. This application may be exemplified in many different forms and should not be construed as being limited to the examples set forth herein.